The invention relates to a charged particles apparatus having a particle source, a lens system and two beam-bounding diaphragms which are imageable one on the other and have therebetween a beam deflection system.
Such an apparatus is known from the article "Double-aperture method of producing variably shaped writing spots for electron lithography", published in Journal Vac. Sci. Techn. 15(3), May-June 1978, pp. 891-895 by M.G.R.Thomson et al; hereinafter referred to as the Thomson article. This article describes an electron beam exposure apparatus in which writing can be done, for example, with four spots by means of two composite beam bounding diaphragms which are imageable one on the other. In the apparatus described the four square spots are in alignment and can be activated independently of each other by an adapted shape of the second diaphragm and a correct superposition.
As compared with the original beam shaper as described in U.S. Pat. No. 3,638,231, patterns can be written more quickly with a structure suitable for that purpose. However, this does not apply to all patterns and certainly not to patterns in which an orthogonal and linear structure has been departed from. In general, and in particular for non-orthogonal or non-linear patterns, such a beam shaping system has too little flexibility and as a result of this often is too slow.
For an apparatus for, for example, the production of integrated circuit elements operating with a beam of charged particles it is desirable, irrespective of the fact whether the production takes place directly or via a mask, that the enlargement, the focus and the position of the source image on the object do not vary when the beam cross-section varies, otherwise the angular aperture of a final lens in the system would be restricted. In particular with direct production, such an apparatus must be quick in operation for which purpose a cross-section of the writing spot adapted optimally to the pattern and short writing pulse switching times are desired. Furthermore, it is of importance that aberrations in the system, for example, spherical aberrations, Boersch effects, trajectory displacement effects and scattered radiation should be reduced as much as possible.